A particle moving in the positive X direction has de Broglie wavelength ${\lambda }_1$. Another particle also moving in the same direction has de Broglie wavelength ${\lambda }_2$. The two particles make a collision and after the collision they move together as a single particle. The de Broglie wavelength of this single particle is given by 

• A

  $\frac{{\lambda }_1+{\lambda }_2}{2}$

• B

  $\sqrt{{\lambda }_1{\lambda }_2}$

• C

  $\frac{2{\lambda }_1{\lambda }_2}{{\lambda }_1 +{\lambda }_2}$

• D

  $\frac{{\lambda }_1{\lambda }_2}{{\lambda }_1 +{\lambda }_2}$